In studies evaluating possible correlations between platelet monoamine oxidase (MAO) activity and behavior, differences in arousal responses and motor activity patterns were found when human newborns with high versus low amine oxidase activities were compared. These characteristics are possibly analogous to behavioral and psychological features which have recently been more explicitly delineated as associated with low MAO activity in normal populations and certain psychiatric patient populations. In laboratory studies of monoamine oxidase, dopamine has been found to be predominantly deaminated by the MAO B subtype in non-human primates and man.